Catalysts which can be used in conversion reactions of hydrocarbons and containing silicon

ABSTRACT

The invention relates to a catalyst comprising: 
     a matrix consisting of 0 and 100% by weight of λ transition alumina, the complement up to 100% by weight of the matrix being in γ transition alumina, and relative to the total weight of the catalyst, 
     from 0.001 to 2% by weight of silicon, 
     from 0.1 to 15% by weight of at least one halogen chosen from the group formed by fluorine, chlorine, bromine and iodine, 
     from 0.01 to 2% by weight of at least one noble metal from the platinum group, from 0.005 to 10% by weight of at least one promoter metal chosen from the group formed by tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, molybdenum and tungsten, and 
     if required from 0.001 to 10% by weight of a doping metal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to catalysts which can be used inconversion reactions for hydrocarbons, in particular in process forreforming gasolines and producing aromatics.

2. Description of the Background

Catalytic reforming is a process which makes it possible to improve theoctane number of the oil fractions and in particular of the heavypetroleum from distillation by conversion of n-paraffins and naphthenesinto aromatic hydrocarbons.

The operation of catalytic reforming thus consists on the one hand oftransforming C₇-C₁₀ n-paraffins into aromatics and light paraffins andon the other hand C₇-C₁₀ naphthenes into aromatics and light paraffins.These reactions are illustrated in particular by the conversion bydehydrogenation of cyclohexanes and the dehydroisomerization ofalkylcyclopentanes to yield aromatics, methycyclohexane yielding forexample toluene, and also by conversion by cyclization of n-paraffinsinto aromatics, n-heptane for example yielding toluene.

During catalytic reforming, cracking reactions also take place of heavyn-paraffins into light paraffins leading in particular to C₁-C₄ productsessentially of propane and isobutane: these reactions are detrimental tothe yield of reformed product.

Finally, there is also the formation of coke through condensation ofaromatic nuclei forming a solid product, rich in carbon which isdeposited on the catalyst.

The reforming catalysts are very sensitive, apart from coke, to variouspoisons which can reduce their activity: in particular sulphur,nitrogen, metals and water.

By being deposited on the surface of the catalyst, the coke brings abouta loss in activity with time which leads to higher operatingtemperatures, a lower yield of reformed products, and a higher gasyield.

Because of this and considering the regeneration of the catalyst, thecatalytic reforming process can be put into operation in two differentways: in a semi-regenerating or cyclic manner and in a continuousmanner. In the first case, the process is carried out with a fixed bed,in the second with a mobile bed.

In the semi-regenerating process, to compensate for the loss of activityof the catalyst, one raises the temperature progressively and then theinstallation is stopped in order to carry out the regeneration of thecatalyst by eliminating the coke. In cyclic reforming which in fact is avariation of the semi-regenerating process, the installation comprisesseveral reactors in series and each is closed down in turn, the cokedeposits are eliminated from the catalyst out of action and the catalystregenerated while the other reactors continue to operate.

In continuous reforming, the reactors put into operation are mobile-bedreactors operating at low pressure (less than 15 bars), which makes itpossible to raise considerably the yields of reformed product andhydrogen by encouraging aromatization reactions instead of cracking, buton the other hand the formation of coke is greatly accelerated. Thecatalyst passes through the reactors then a regenerating action.

The processes for production of aromatics imply conversion reactions ofthe paraffinic and naphthenic hydrocarbons into aromatic compounds.

In these hydrocarbon conversion processes, there are generally usedbi-functional catalysts containing, for example, platinum and a supportof chlorinated alumina, which associate the acidic function of thechlorinated alumina necessary for the reactions of isomerization ofcyclopentanic naphthenes and the cyclization of paraffins with thedehydrogenating function of the platinum necessary for thedehydrogenation reactions. Catalysts of this type, also includinganother metal such as rhenium, tin or lead, are described in US-A-3 700588 and US-A-3 415 737.

As can be seen from the above, the catalytic reforming processes can becarried either by using a fixed bed or a mobile bed of catalyst.

In each case, the catalyst undergoes a regenerating treatment operatingat high temperature and in the presence of steam, which consists amongother things of burning off the coke deposited on the catalyst.Unfortunately, these treatment conditions favour degradation of thecatalyst. It is thus important to try to raise the resistance of thecatalyst under these conditions.

Generally the catalyst is presented in the form of extrusions or ballsof a sufficient size to let the reagents and gaseous products passrelatively easily. Wear of the catalyst results, in particular throughfriction in processes with mobile beds, which provokes the formation ofdusts and finer grains. These very fine grains perturb the gaseous flowand require raising the entry pressure of the reagents and even, incertain cases, to stop the unit. In mobile bed units, this progressivewear also has the consequence of perturbing the circulation of thecatalyst and makes it necessary to top up the catalyst frequently.

A catalyst like a reforming catalyst must thus satisfy a great number ofrequirements, certain of which may appear contradictory. This catalystmust first of all provide the greatest activity possible allowing highyields to be obtained, but this activity must also be conjugated withthe greatest selectivity possible, that is to say that crackingreactions leading to light products containing from 1 to 4 carbon atomsmust be limited.

In addition, the catalyst must be highly stable vis-a-vis itsdeactivation through coke deposit; the catalyst must also have excellentresistance to degradation when it is submitted to the extreme conditionsexisting in the repeated regenerating operations it has to undergo.

In the case of the continuous reforming process operating for mobile bedreactors and as mentioned above, the catalysts are also submitted tointense and progressive wear through friction, which leads to aconsiderable diminution of their specific surface area and the formationof “smalls” which prejudice the functioning of the installation. Thecatalysts available at present, even if they can fulfill one or severalof these conditions, do not satisfy the whole range of the requirementsmentioned above.

Also, despite the many improvements already made to the bi-functionalcatalysts used, there is still a need for new catalysts offeringimproved performance, not only as far as the yield of conversionreactions is concerned, but also the lifespan of the catalyst.

SUMMARY OF THE INVENTION

The present invention concerns precisely a multi-functional catalystwhich presents improved catalytic performance and an extended lifespanin reactions of reforming and production of aromatics.

According to the invention, the catalyst comprises:

a matrix constituted of 0 to 100% by weight of λ transition alumina, thecomplement to 100% by weight of the matrix being γ transition alumina,and

compared with the total weight of the catalyst,

from 0.001 to 2% by weight of silicon,

from 0.1 to 15% by weight of at least one halogen chosen from among thegroup formed by fluorine, chlorine, bromine and iodine,

from 0.01 to 2% by weight of at least one noble metal of the platinumgroup,

from 0.005 to 10% by weight of at least one promoter metal chosen fromthe group formed by tin, germanium, indium, gallium, thallium, antimony,lead, rhenium, manganese, chromium, molybdenum and tungsten, and it hasundergone a complementary hydrothermal treatment, at a temperature from300 to 1000° C., in a gaseous atmosphere containing steam.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention, the catalyst comprises in additionfrom 0.001 to 10% by weight of at least one doping metal chosen from thegroup constituted of the alkali and alkaline-earth metals, thelanthanides, titanium, zirconium, hafnium, cobalt, nickel and zinc.

It is to be noted that in the continuation of this text all the contentsof silicon, halogen, noble metal, promoter metal and doping metal areexpressed in weight % compared to the total weight of the catalyst,unless indicated to the contrary. Moreover, these content levelscorrespond to the total content of constituent (doping metal, halogen,noble metal or promoter metal) when the constituent comprises severalelements (halogens or metals).

In the invention, the application of a complementary hydrothermaltreatment of the catalyst is very important. In fact, in the catalystsof the invention, it has been noted that the presence of siliconpreserves the matrix in alumina(s) of the catalyst from a loss ofspecific surface area when it is submitted to the regenerationtreatments necessary for its operation in conversion reactions ofhydrocarbons, but the catalyst with silicon has the disadvantage ofproducing a high degree of cracking. In unexpected fashion, theapplicant has noted that every complementary hydrothermal treatment inthe presence of water applied to this type of catalyst has the effect ofpreserving the loss of specific surface area, while also improvingcatalytic performance (less cracking).

Preferably, this complementary hydrothermal treatment is carried out ina gaseous atmosphere containing not only steam but also a halogen suchas chlorine.

A preferred catalyst of the invention comprises:

a support constituted of a matrix of γ alumina, of λ alumina or of amixture of γ alumina and λ alumina plus silicon.

at least one halogen,

a catalytic metal ensuring the function of dehydrogenation of thecatalyst, constituted of one or several noble metals of the platinumgroup, and

at least one promoter metal chosen from among the metals cited above.

In the invention the matrix is a base of a hydrated oxide of aluminium.It is known that supports in alumina of the general-formula Al₂O₃, nH₂O,where n goes from 0 to 0.6, which present a specific surface area of 150to 400 m²/gm, can be obtained by controlled dehydration of amorphousaluminium hydroxides where n has a value of between 1 and 3. Theoriginal amorphous hydroxides can exist under several forms and the mostcommon are boehmite (n=1) gibbsite and bayerite (n=3), and they can leadduring dehydration treatment to several transition oxides or aluminassuch as the forms ρ, γ, λ, χ, θ,δ,κ, and α which are differentiatedessentially by the organization of their crystalline structure. Duringthermal treatments, these different forms are susceptible to evolutionbetween themselves, following a complex relationship which depends onthe operating conditions of the treatment. The a form which presents aspecific surface area and acidity which are nearly zero, is the moststable at high temperatures. For reforming catalysts, the y form oftransition alumina is used most often, because of the compromise itoffers between its properties of acidity and thermal stability.

In the invention, γ transition alumina, λ transition alumina orpreferably a mixture of γ transition alumina and λ transition alumina isused.

λ transition alumina can be obtained by roasting bayerite in dry air, atatmospheric pressure, between 250 and 500° C., preferably between 300and 450° C. The specific surface area achieved which depends on thefinal temperature of roasting, is between 300 and 500 m²/gm. The γalumina comes from boehmite through roasting under air at a temperaturebetween 450 and 600° C. The specific surface area of the γ aluminaobtained is between 100 and 300 m²/gm.

These two transition aluminas have crystalline structures which areclose but distinctive. The technique of X-ray diffraction can, inparticular, differentiate between them. Their structures are of thespinel type with faults, and their networks are slightly distant fromcubic symmetry. This quadratic deformation is minimal for the λ form andis much clearer for γ alumina whose unit-cell parameters are as follows:a=b=7.95 Å and c=7.79 Å.

According to the invention, when using a mixture of γ transition aluminaand λ transition alumina, this mixture can comprise from 0.1 to 99% orrather from 1 to 84% by weight of λ alumina. Preferably, this mixturecomprises 3 to 70% by weight, and even better 5 to 50% by weight of λtransition alumina, the complement to reach 100% by weight of themixture being γ transition alumina.

According to the invention, the alumina matrix is modified by silicon.

The content of silicon of the catalyst is between 0.001 to 2% by weight,preferably 0.01 to 1% by weight.

The halogen or halogens used to acidify the support can represent atotal of 0.1 to 15% by weight, and preferably 0.2 to 10% by weight.Preferably, a single halogen is used, in particular chlorine.

The catalyst also comprises one or several promoter metals which havethe effect of promoting the dehydrogenation activity of the noble metalof the platinum group and of limiting the dispersion loss of the atomsof the noble metal from the support surface, which is partly responsiblefor the deactivation of the catalyst.

The total content of promoter metals is 0.005 to 10% by weight,preferably 0.01 to 1% by weight.

The promoter metals are chosen in function of the method of utilizationof the catalyst.

Thus, when the catalyst is to be used in a fixed bed process, thepromoter metal is chosen preferably from the group constituted byrhenium, manganese, chromium, molybdenum, tungsten, indium and thallium.

When the catalyst is to be used in a mobile bed process, the promotermetal is chosen preferably from the group constituted by tin, germanium,indium, antimony, lead, thallium and gallium.

Among these, rhenium is preferred for fixed bed processes and tin formobile bed processes, since they produce the best promoter effects onthe catalyst activity.

In particular, rhenium increases the stability of the catalyst vis-à-visits deactivation by coke deposits. Thus, preferably, rhenium is used incatalysts for fixed bed units since this added stability makes itpossible to lengthen the reactive cycles between two catalystregenerations.

As far as tin is concerned, this makes it possible to improve theperformance of catalysts when they are used at low pressure. Thisimprovement together with the lower cracking activity of catalysts usingtin permits improved yields of reformed product, above all in continuousregeneration processes on mobile beds functioning at low operatingpressure.

The total promoter metal content is from 0.005 to 10% by weight,preferably 0.01 to 1% by weight.

When the catalyst only contains a single promoter metal, for examplerhenium or tin, it is preferably present at 0.005 to 0.9% by weight or,even better, at 0.01 to 0.8% by weight.

The catalyst according to the invention comprises as well at least onenoble metal of the platinum group, 0.01 to 2% by weight, and preferably0.1 to 0.8% by weight.

The noble metals which can be used are platinum, palladium, iridium;platinum is to be preferred.

According to one embodiment of the invention, the catalyst comprises inaddition 0.001 to 10% by weight of at least one doping metal chosen fromthe group constituted by the alkali and alkaline-earth metals,lanthanides, titanium, zirconium, hafnium, cobalt, nickel and zinc.

In this case, the alumina matrix is modified with silicon and one orseveral doping metals.

Preferably, the doping metals belong to just one of the followinggroups:

1)—the group of alkali and alkaline-earth metals,

2)—the group of lanthanides, and

3)—the group comprising titanium, zirconium, hafnium, cobalt, nickel andzinc.

In the case of metals belonging to the first group (alkali andalkaline-earth metals) the total content of doping metal of the catalystis generally 0.001 to 8% by weight.

The alkali metals used can be lithium, sodium, potassium, rubidium andcaesium; the alkaline-earth metals can be chosen from among beryllium,magnesium, calcium, strontium and barium.

The content of doping metal of the first group is chosen in particulardepending on the reactor in which the catalyst of the invention will beused.

Thus, in the case of a fixed bed reactor, the content of doping metal ofthe catalyst is generally within the range of 0.001 to 0.3%, andpreferably between 0.005 and 0.3% or even better 0.01 and 0.3% byweight.

In the case of a reactor with mobile bed, the content of doping metal ofthe catalyst is higher, generally from more than 0.3 to 8%, preferablymore than 0.3 to 4% and even better 0.7 to 4% by weight.

Preferably, the doping metal is an alkali metal such as potassium.

In the case of doping metals belonging to the second group(lanthanides), the total content of doping metal of the catalyst can befrom 0.001 to 10% by weight.

The group of lanthanides or rare earths is comprised of the elements ofthe lanthanum group in the Mendeleev periodic table and whose atomicnumbers are between 57 and 71, for example lanthanum, cerium, neodymiumand praseodymium.

The total content of doping metal of the second group is chosen inparticular depending on the reactor in which the catalyst will be used.

Thus, it can be preferably between 0.001 to 0.5% and even better 0.01 to0.5% by weight when the catalyst is used in a fixed bed process.Preferably, it is from more than 0.5 to 10%, or even better from morethan 0.5 to 4% by weight when the catalyst is used in a mobile bedprocess.

In the case of doping metals belonging to the third group (Ti, Zr, Hf,Co, Ni, Zn), the total content of doping metal of the catalyst can befrom 0.001 to 10% by weight.

It can also be chosen in function of the reactor in which the catalystis to be used.

Thus, the total content of doping metal of the third group is,preferably, from 0.001 to 0.7% and even better from 0.01 to 0.7% byweight when the catalyst is used in a fixed bed process. Preferably, itis more than 0.7 to 10% and even better more than 0.7 to 4% by weightwhen the catalyst is used in a mobile bed process.

The catalyst of the invention can be prepared by depositing itsdifferent constituents on the alumina matrix. The deposit of eachconstituent can be carried out totally or partially on one or both ofthe two aluminas of the matrix before or after it is formed. Theconstituents can be deposited separately or simultaneously in any order.

Thus, when a mixture of aluminas is used as the matrix, the constituentsof the catalyst can be deposited on the two aluminas or on one of them,preferably the λ alumina, before carrying out the mixture of the twoaluminas and forming them.

It is also possible to deposit one or certain constituents partly ortotally on the two aluminas or one of them before mixing them, thencarry out the other deposits after mixing of the two aluminas, eitherbefore or after the forming of the mixture. When one or severalconstituents is (are) deposited before mixing the two aluminas, siliconis preferably deposited on the transition alumina.

However, according to the invention, it is generally preferred to mixthe two aluminas before depositing the metallic constituents and thehalogen(s).

The invention also concerns a process for preparing the catalyst of theinvention, which comprises the following stages:

a) eventual preparation by mixing and then by forming of a matrix in γtransition alumina, in λ transition alumina, or in a mixture of λtransition alumina and γ transition alumina.

b) deposit on at least one of the γ and λ transition aluminas of one ofthe following constituents, in the weight percentages given below, whichrefer to the total weight of the catalyst;

from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight, ofsilicon,

from 0.1 to 15%, preferably 0.2 to 10% by weight of at least one halogenchosen from the group constituted by fluorine, chlorine, bromine andiodine,

from 0.01 to 2% of at least one noble metal of the platinum group, and

from 0.005 to 10% by weight of at least one promoter metal chosen fromthe group constituted by tin, germanium, indium, gallium, thallium,antimony, lead, rhenium, manganese, chromium, molybdenum and tungsten,

from 0.001 to 10% by weight if required of at least one doping metalchosen from the group constituted by the alkali and alkaline-earthmetals, lanthanides, titanium, zirconium, hafnium, cobalt, nickel andzinc.

Stages a) and b) can be carried out in any order and the deposits ofstage b) can be only partly carried out before stage a) and can becarried out in any order; and

c) complementary hydrothermal treatment of the catalyst obtained afterstages a) and b), at a temperature between 300 and 1000° C., in agaseous atmosphere containing steam.

In a preferred embodiment of this process, a support formed from thematrix of alumina and silicon is first prepared, then the doping metalor metals is or are deposited thereon, the promoter metal or metals, thehalogen or halogens, and the noble metal or metals of the platinumgroup.

In this case, silicon can be deposited on the alumina or the mixture ofaluminas, before or after forming.

Preferably, the silicon is deposited after the forming of the aluminamatrix.

Also, the invention relates to the support obtained in the first stageof this preferred process, which is constituted of a matrix comprising 0to 100% by weight of λ transition alumina, the complement making up the100% by weight of the matrix being γ transition alumina, and silicon,the quantity of silicon being from 0.001 and 2.7% and preferably from0.01 to 1.35% by weight of silicon compared with the weight of thesupport.

The deposit of the different constituents of the catalyst can be carriedout by classical techniques, in liquid or gaseous phase, starting fromthe appropriate precursor components. When the deposit is made on thealumina matrix which is already formed, the techniques employed can forexample be dry impregnation, impregnation through excess solution orionic-exchange. This operation is followed if necessary by drying androasting at a--temperature-between 300 and 900° C., preferably in thepresence of oxygen.

Thus, the silicon can be deposited from components such as the alkyltetraorthosilicates, the silicon alkoxides, the quaternary ammoniumsilicates, the silanes, the disilanes, the silicones, the siloxanes, thesilicon halides, the halogenosilicates and silicon in the form ofmicro-balls of colloidal silica. In the case where the precursor ofsilicon is a fluorosilicate, this can be expressed by the formulaM₂/xSiF₆, where M is a metallic or non-metallic cation with valency x,chosen from among the following cations: NH₄ ⁺, ammonium alkyls, K⁺,Na⁺, Li⁺, Ba²⁺, Mg²⁺, Cd²⁺, Cu+, Cu²⁺, Ca²⁺, Cs⁺, Fe²⁺, Co²⁺, Pb²⁺,Mn²⁺, Rb⁺, Ag⁺, Sr²⁺, Zn²⁺, Tl⁺ and H⁺.

When the silicon is deposited after the forming of the alumina matrix,this deposit is preferably carried out by impregnation in a water mediumby using an excess of aqueous solution of the precursor Then theimpregnation solvent is eliminated, for example by drying and airroasting is carried out, at a temperature for example between 300 and900° C.

The deposit of the doping metal or metals of the first group chosen fromamong the alkali and alkaline-earth metals can be carried out by anytechnique and can take place at any stage of the preparation process ofthe catalyst. When the deposit is made after the forming of the matrixof alumina, it is preferable to use impregnation in an aqueous medium byexcess of solution, followed by drying to eliminate the impregnationsolvent and roasting in air at a temperature between for example 300 and900° C.

The precursor components used can be for example salts of the alkali andalkaline-earth metals such as halides, nitrates, carbonates, acetates,sulphates, cyanides and oxalates.

The deposit of doping metal or metals of the second group (lanthanides)can be carried out using any technique known to the state of the art,and can take place at any moment of the preparation of the catalyst. Forexample, when this element of the group of the lanthanides or rareearths is deposited after forming the alumina or aluminas containingother metals, if required, dry impregnation, impregnation through excessof solution or ionic exchange can be used. On a matrix which has alreadybeen formed, a preferred method for the introduction of this additionalelement is impregnation in an aqueous medium by using an excess ofsolution. In order to eliminate the impregnation solvent, thisimpregnation is followed by drying and roasting in air at a temperaturebetween, for example, 300 and 900° C.

The precursor components can be, for example, halides, nitrates,carbonates, acetates, sulphates or oxalates of said elements.

The deposit of doping metal or metals of the third group composed oftitanium, zirconium, hafnium, cobalt, nickel and zinc on the matrix ofthe catalyst used in the present invention, can be carried out accordingto all the state of the art techniques, and can occur at any momentduring the preparation of the catalyst. For example, when this elementis deposited after forming of alumina or aluminas containing, ifrequired, other metals, dry impregnation, impregnation through excesssolution, or ionic exchange can be used. On a matrix which is alreadyformed, a preferred method for introducing this additional element isimpregnation in an aqueous medium by using an excess of solution. Inorder to eliminate the impregnation solvent, this impregnation isfollowed by drying and roasting in air at a temperature of between, forexample, 300 and 900° C.

The deposits of silicon and at least one element chosen from the groupconstituted by titanium, zirconium, hafnium, cobalt, nickel and zinc canbe carried out independently from each other, either on a transitionalumina or on the non-formed matrix, said matrix comprising between 0and 99% by weight of λ transition alumina and the complement up to 100%of γ transition alumina, or yet again on the preformed matrix, thelatter being the preferred method.

The deposit of a noble metal or metals of the platinum group can also becarried out by classical techniques, in particular impregnation from anaqueous solution or not containing a salt or compound of the noblemetal. As an example of salts or compounds which can be used,chloroplatinic acid, ammoniated compounds, ammonium chloroplatinate,platinum dicarbonyl dichloride, hexahydroxyplatinic acid, palladiumchloride and palladium nitrate may be mentioned.

In the case of platinum, the ammoniated compounds can be for example thesalts of platinum IV hexamines of formula Pt(NH₃)₆X₄, the salts ofplatinum IV halogenopentamines of formula (PtX(NH₃)₅)X₃, the salts ofplatinum tetrahalogenodiamines of formula PtX₄(NH₃)₂X, the complexes ofplatinum with halogens- polyketones and the halogen compounds of formulaH (Pt (aca)₂X) in which the element X is a halogen chosen from the groupcomprising chorine, fluorine, bromine and iodine, and preferablychlorine, and the aca group represents the rest of the formula C₅H₇O₂derived from acetylacetone. The introduction of the noble metal of theplatinum group is preferably carried out by impregnation using anaqueous or organic solution of one of the organometallic compounds citedabove. Among the organic solvents which can be used, the paraffin,naphthene or aromatic hydrocarbons may be mentioned, and the halogenatedorganic compounds with for example 1 to 12 carbon atoms per molecule.For example n-heptane, methylcyclohexane, toluene and chloroform can bementioned. Solvent mixtures may also be used.

After introduction of the noble metal, drying and roasting is preferablycarried out, for example, at a temperature of between 400 and 700° C.

The depositing of a noble metal or noble metals of the platinum groupcan be made at any time during the preparation of the catalyst. It canbe carried out in isolation or simultaneously with the depositing ofother constituents, for example of the promoter metal or metals. In thislatter case, a solution containing all the constituents to be introducedsimultaneously may be used for impregnation.

The deposit of the promoter metal or metals can also be carried out byclassical techniques beginning from precursor compounds such as thehalogens, nitrates, acetates, tartrates, citrates, carbonates and theoxalates of these metals. Any other salt or oxide of these metals whichis soluble in water, acids, or in another appropriate solvent, is alsosuitable as a precursor. As examples of such precursors, mention can bemade of the rhenates, chromates, molybdates and tungstates. The promotermetal or metals can also be introduced in the mixture in an aqueoussolution of their precursor compound(s) with the alumina or aluminasbefore formation, followed by roasting in air at a temperature between400 and 900° C.

The introduction of promoter metal or metals can also be carried outwith the aid of a solution of an organometallic compound of said metalsin an organic solvent. In this case, this deposit is preferably carriedout after that of the noble metal(s) of the platinum group and roastingof the solid, followed if required by reduction with hydrogen at hightemperature, for example between 300 and 500° C. The organometalliccompounds are chosen in the group constituted by the complexes of saidpromoter metal, in particular the polyketone complexes and thehydrocarbylmetals such as the alkyl, cycloalkyl, aryl, alkylaryl andarylalkyl metals. Organohalogen compounds may also be used. Mention canbe made in particular of tin tetrabutyl in the case where the promotermetal is tin, lead tetraethyl in the case where the promoter metal islead and indium triphenyl in the case where the promoter metal isindium. The impregnation solvent can be chosen from the groupconstituted by the paraffinic, naphthenic or aromatic hydrocarbonscontaining from 6 to 12 carbon atoms per molecule and the halogenorganic compounds containing 1 to 12 atoms of carbon per molecule.Mention can be made for example, of n-heptane, methylcyclohexane andchloroform. Mixtures of the solvents defined above can also be used.

The halogen, for example chlorine, can be introduced into the catalystat the same time as another metallic constituent, for example in thecases where a halide is used as precursor compound of the metal of theplatinum group, of the promoter metal or of the alkali or alkaline-earthmetal. This introduction can also be carried out through impregnation ofthe support by means of an aqueous solution containing an acid or ahalogenated salt. For example, chlorine can be deposited by using asolution of hydrochloric acid. The introduction of chlorine can also becarried out by roasting of the catalyst at a temperature between forexample 400 and 900° C., in the presence of an organic compoundcontaining the halogen, such as for example CCl₄, CH₂Cl₂ and CH₃Cl.

Of course, at least two constituents of the catalyst can be introducedsimultaneously, for example from a solution containing their precursorcompounds.

The constituents can also be introduced successively, from separatesolutions, in any order. In this latter case, intermediary drying and/orroasting can be carried out.

The formation of the alumina matrix can be carried out using state ofthe art techniques for formation of catalysts such as, for example,extrusion, drip coagulation, coating, drying by atomization orpelleting.

In the preferred embodiment, the preparation process is characterized inthat it comprises the is following successive stages:

a) formation of the matrix of γ alumina or λ alumina or of a mixture ofγ alumina and λ alumina,

b) deposit of silicon on this matrix,

c) possible deposit of at least one doping metal, and

d) simultaneous or successive deposit

of at least one promoter metal chosen from among tin, germanium, indium,gallium, thallium, antimony, lead, rhenium, manganese, chromium,molybdenum and tungsten;

of at least one element chosen from the group constituted by fluorine,chlorine, bromine, iodine, and

of at least one noble metal of the platinum group.

After formation of the matrix and deposit of all the constituents, afinal thermal treatment can be carried out between 300and 1000° C.;which can comprise only a single stage preferably at a temperaturebetween 400 and 900° C., and in an atmosphere containing oxygen,preferably in the presence of free oxygen or air. This treatmentgenerally corresponds to drying-roasting following the deposit of thelast constituent.

After formation of the matrix and deposit of all the constituents, thecomplementary hydrothermal treatment is carried out at a temperaturebetween 300 and 1000° C. and preferably 400 to 700° C., in a gaseousatmosphere containing steam and, if required, a halogen such aschlorine.

This treatment can be carried out on a bed crossed by a current of gasor in a static atmosphere. Preferably, the gaseous atmosphere containswater and if required at least one halogen. The molar content in wateris from 0.05 to 100%, preferably 1 to 50%. The molar content of halogenis 0 to 20%, and preferably between 0 and 10%, and preferably againbetween 0 and 2%. The duration of treatment is variable depending on theconditions of temperature, partial water pressure and quantity ofcatalyst. Advantageously, this value is between one minute and 30 hours,preferably between 1 and 10 hours. The gaseous atmosphere used is forexample based on air, oxygen, or an inert gas such as argon or nitrogen.

The role of this high-temperature treatment in the presence of water isimportant. As described in the examples given below, in the presence ofsilicon which preserves the matrix in alumina(s) from a loss of specificsurface area during the different regenerating treatments, in anunexpected fashion, harsh thermal treatment in the presence of waterapplied to this type of catalyst has the effect of preserving it from aloss of specific surface area, while still improving the catalyticperformance.

After the final thermal treatment, the catalyst can be subjected to anactivation treatment under hydrogen at high temperature, for example ata temperature between 300 and 550° C.

The process for treatment under hydrogen consists for example of raisingthe temperature slowly in a current of hydrogen until the maximumreduction temperature is reached, generally between 300 and 550° C. andpreferably between 350 and 450° C., followed by maintenance at thistemperature for a period which generally lasts between 1 and 6 hours.

The catalyst of the invention can be used in particular in reactions forconversion of hydrocarbons, and more particularly in the processes ofreforming of gasolines and production of aromatics.

The reforming processes make it possible to raise the octane number ofthe gasoline fractions from the distillation of crude oil and/or otherrefining processes.

The processes for production of aromatics provide the bases (benzene,toluene and xylene) which can be used in petrochemistry These processeshave a supplementary interest in that they contribute to the productionof large quantities of hydrogen which are indispensable for thehydrotreatment, processes of the refinery.

These two processes differ through the choice of operating conditionsand the composition of the load.

The typical load treated by these processes contains paraffinic,naphthenic and aromatic hydrocarbons containing 5 to 12 atoms of carbonper molecule. This load is defined, among other things, by its densityand its composition by weight.

In order to activate these processes, the hydrocarbon load is placed incontact with the catalyst of the present invention, at a temperature of400 to 700° C., using the mobile bed or fixed bed technique.

Generally the mass flow of the charge treated per unit mass of thecatalyst is between 0.1 and 10 kg/kg.hr. The operating pressure can befixed between atmospheric pressure and 4 MPa.

A part of the hydrogen produced is recycled according to a molarrecycling content of between 0.1 and 8. This content is the molarrelation of the flow of hydrogen recycled over the mass flow of load.

Other features and advantages of the invention will become clearer whenreading the examples which follow, it being understood that the datagiven are illustrative and non-restrictive.

EXAMPLE 1

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and λ alumina, on which silicon,chlorine, tin and platinum are deposited.

a) Formation of the Alumina Matrix

First of all, the alumina matrix is prepared by mixing a powder of γalumina of a specific surface area of 220 m²/gm and a powder of λalumina with a specific surface area equal to 320 m²/gm which has beenprepared by roasting of bayerite. The proportion of λ alumina is 10% byweight. This mixture is then formed by extrusion, then roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byplacing it into contact with an ethanolic solution of tetraethylorthosilicate (Si(OC₂H₅)₄. The concentration of this solution is 18.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours. Onethus obtains a support conforming to the invention.

c) Deposit of Platinum, Tin and Chlorine

Next, platinum, tin and chlorine are simultaneously deposited on thesupport by impregnation with an aqueous chlorinated solution containingper liter:

0.81gm of platinum under the form H₂PtCl₆, and

0.96gm of tin under the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

d) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. To do so, the catalyst is treated at 510° C. for 2 hoursin a current of 2000 dm³/hr of air for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 1.

EXAMPLE 2

The same operating mode as in example 1 is followed in order to preparea catalyst comprising the same constituents, except that thehydrothermal treatment of stage d) is not performed.

The specifications of the catalyst obtained are also given in table 1.

COMPARATIVE EXAMPLE 1

In this example, the same operating mode as in example 1 is followed butin stage a) only γ alumina is used, and stage b) for depositing siliconand stage d) for hydrothermal treatment are not performed.

The specifications of the catalyst obtained are also given in table 1.

TABLE 1 Proportion η alumina Specific Platinum Tin Chlorine Silicon(weight % surface content content content content in the area (weight(weight (weight (weight Catalyst matrix) (m²/gm) %) %) %) %) Ex- 10 2270.25 0.17 1.08 1.04 ample 1 Ex- 10 228 0.24 0.18 1.13 1.02 ample 2 Com-0 219 0.23 0.18 1.15 0 par- ative Ex- ample 1

EXAMPLE 3

In this example, the catalysts of examples 1 and 2 and of thecomparative example, are tested for conversion of a load of hydrocarbonswith the following specifications:

volume mass at 20° C. 0.736 kg/dm³ octane number required ˜38 content ofparaffins 54.8% by weight content of naphthenes 33.1% by weight contentof aromatics 12.1% by weight

The following operating conditions are used:

temperature 500° C. total pressure 1.0 Mpa mass flow of load 1.8 kg/kgof catalyst duration 100 hr. total pressure 1/0 MPa throughput of load1.8 kg/kg of catalyst duration 100 hours

At the end of the operating period, the deactivated catalyst isregenerated by controlled combustion of the coke and adjustment of itschlorine content to about 1.10% by weight. The specific surface of thesupport is measured after this regeneration. Then, after activation ofthe catalyst at high temperature by hydrogen, the load is injected for anew period of operation. In this way, each catalyst has been subjectedto 5 operation/regeneration cycles. the specific surfaces correspondingto the start of the first and of the last cycle and the performanceobtained after 15 hours of operation in each of these two cycles arereported in Table 2 below. reformed product. It is also noted that theseimprovements are achieved without the yields of reformed-product beingaffected.

If the evolution over 5 cycles is now considered, it can be seen thatthe lowering of the specific surface areas of examples 1 and 2 is muchless than that of the prior art catalyst. This smaller fall isaccompanied by greater stability of yields in aromatics and of octanenumbers.

The catalysts of the invention thus make it possible to obtain, in astable way over several cycles, better octane numbers for unchangedyields of reformed product.

EXAMPLE 4

This example illustrates the production of a catalyst comprising amatrix formed of a mixture or γ alumina and λ alumina, on which silicon,chlorine, potassium, rhenium and platinum are deposited.

a) Formation of the Matrix in Alumina

The alumina matrix is first prepared by mechanically mixing a powder ofγ alumina of specific surface area of 220 m²/gm and a powder of λalumina of specific surface area equal to 320 m²/gm which has beenprepared by roasting of bayerite. The λ alumina proportion is 30% byweight. This mixture is then formed by extrusion, and roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byplacing it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at room temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Potassium Deposit

Then the extrusions are put into contact with an aqueous solution ofpotassium carbonate K₂CO₃ containing 12.8 gm/l of potassium. Thiscontact is carried out at ambient temperature for 1 hour, and then theimpregnated matrix is dried at 120° C. over 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

The platinum and part of the chlorine are then deposited simultaneouslyon this support through impregnation by a chlorinated aqueous solutioncontaining per liter:

8.20 gm of chlorine in the form of HCl, and 1.00 gm of platinum in theform of H₂PtCl₆. The solution is left in contact with the support for 2hours. After centrifugation and drying for 4 hours at 120° C., theimpregnated support is roasted at 530° C. for 3 hours in a current ofdry air

e) Deposit of Rhenium and Chlorine

Then, the rhenium and the rest of the chlorine are simultaneouslydeposited through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a current of dry air.

f) Hydrothermal Treatment

Then a hydrothermal treatment in the presence of water and chlorine iscarried out. To do so, the catalyst is treated at 510° C. for 2 hours ina current of air of 2000 dm³/hr for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 3.

EXAMPLE 5

The same operating mode as in example 4 is followed to prepare acatalyst comprising the same constituents, apart from the fact that instage c), the impregnation solution contains 6.4 gm/l of potassium, andthe hydrothermal treatment of stage e) is not carry out.

The specifications of the catalyst obtained are also given in table 3.

COMPARATIVE EXAMPLE 2

In this example, the same operating mode as in example 4 is followed butonly γ alumina is used in stage a), and stages b) and c) for depositingsilicon and potassium and stage f) for hydrothermal treatment are notcarried out.

The specifications of the catalyst obtained are also given in table 3.

EXAMPLE 6

This example illustrates the production of a catalyst comprising amatrix formed from a mixture of γ alumina and λ alumina comprising 8% ofλ alumina, on which silicon, chlorine, potassium, tin and platinum aredeposited.

For this preparation, the same operating mode as in example 4 isfollowed, utilizing in stage a) 8% by weight of λ=0 alumina and, insteadof stages d) and e), carrying out a single simultaneous deposit stage ofplatinum, tin and chlorine through impregnation with a chlorinatedaqueous solution containing per liter:

0.81gm of platinum in the form H₂PtCl₆, and

0.96gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air

A hydrothermal treatment in the presence of water and chlorine is thencarried out, as in stage f) of example 4.

The specifications of the catalyst obtained are given in table 3.

EXAMPLE 7

The same operating mode as in example 6 is s followed to prepare acatalyst comprising the same constituents, apart from the fact that, instage c), the impregnation solution contains 6.4 gm/l of potassium, andthe final hydrothermal treatment in the presence of water and chlorineis not carried out.

The specifications of the catalyst obtained are also given in table 3.

COMPARATIVE EXAMPLE 3

In this example, the same operating mode as in example 6 is followed,but only γ alumina is used in is stage a), and stages b) and c) fordepositing silicon and potassium and the last stage f) :-or hydrothermaltreatment in the presence of water and chlorine as described in example1 are not carried out.

The specifications of the catalyst obtained are also given in table 3.

TABLE 3 Proportion Specific Platinum Tin Rhenium Chlorine SiliconPotassium η alumina surface content content content content contentcontent (weight % area (weight (weight (weight (weight (weight (weightCatalyst of matrix) (m²/gm) %) %) %) %) %) %) Example 4 30 237 0.25 00.47 1.17 0.045 0.23 Example 5 30 238 0.24 0 0.50 1.07 0.045 0.12Compar. 0 216 0.23 0 0.48 1.12 0 0 Example 2 Example 6 8 227 0.22 0.18 01.14 0.13 0.76 Example 7 8 225 0.25 0.16 0 1.06 0.15 0.34 Compar. 0 2190.23 0.18 0 1.15 0 0 Example 3

EXAMPLE 8

In this example, the catalysts of examples 4 and 5 and of thecomparative example 2 are tested for conversion of a load ofhydrocarbons with the following specifications:

volume mass at 20° C. 0.742 kg/dm³ octane number required ˜41 content ofparaffins 52.2% by weight content of naphthenes 32.4% by weight contentof aromatics 15.4% by weight

The following operating conditions are used:

temperature 500° C. total pressure 1.5 Mpa mass flow of load 2.0 kg/kgof catalyst and per hr. duration 100 hr.

The performances of the catalysts are recorded in table 4 below, and areexpressed in yields by weight and of the octane number required of thereformed product.

TABLE 4 Yield of re- Hydro- formed gen product yield Aromatics C4(weight (weight yield yield C4 Catalyst %) %) (weight %) (weight %)aromatics Example 4 85.1 3.2 60.2 11.7 0.19 Example 5 84.7 3.3 60.8 12.00.20 Comparative 83.9 3.0 60.0 13.1 0.22 example 2

When comparing the performances of the catalysts of example 4 and thecomparative example 2 on the one hand, and those of the catalysts ofexample 5 is and of the comparative example 2 on the other, it can benoted that the catalysts of examples 4 and S have performances which area clear improvement over the prior art catalyst (comparative example 2).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 4 and 5 are very significantlylower than those observed for the catalyst of the comparative example 2.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4-/aromaticsin the table above, is lower for the two catalysts according to theinvention. The selectivity of the catalysts vis-a-vis the aromaticproducts required become higher as this relation becomes lower.

The catalysts of examples 4 and 5 containing, in addition compared tothe catalyst of example 2, λ alumina, silicon and potassium, showimproved specifications relative to the catalyst of comparative example2, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

EXAMPLE 9

In this example, the catalysts of examples 6 and 7 and of thecomparative example 3 are tested for conversion of a load ofhydrocarbons with the following specifications:

volume mass at 20° C. 0.736 kg/dm³ octane number-required ˜38 content ofparaffins 54.8% by weight content of naphthenes 33.1% by weight contentof aromatics 12.1% by weight

The following operating conditions are used:

temperature 495° C. total pressure 0.75 Mpa mass flow of load 1.8 kg/kgof catalyst duration 100 hr.

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performance obtained after 15 hours of operation for each of thesetwo cycles are recorded in table 5 below.

TABLE 5 Aro- Specific Yield of matics C4 surface reformed Octane yieldyield area product number (weight (weight Catalyst cycle (m²/gm) (weight%) required %) %) Example 6 1 227 91.2 97.9 68.2 5.5 5 220 92.1 96.867.3 4.7 Example 7 1 225 91.2 97.6 67.9 5.4 5 213 91.5 96.5 66.5 5.3Comparative 1 219 90.7 97.5 67.2 6.0 Example 3 5 198 91.6 95.4 65.1 5.2

When comparing the performances of the catalysts of examples 6 and 7,with those of the prior art catalyst (comparative example 3), it can beseen that the catalysts of examples 6 and 7 show better yields inaromatics and better octane numbers for the reformed product. It canalso be noted that these improvements are achieved without the yields ofreformed product being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 6 and 7 is much lessthan that of the prior art catalyst. This smaller fall is accompanied bybetter maintenance of yields in aromatics and octane numbers.

EXAMPLE 10

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and λ alumina, on which silicon,chlorine, lanthanum, rhenium and platinum are deposited.

a) Formation of the Matrix in Alumina

The alumina matrix is first prepared by mechanical mixing of a powder ofγ alumina of specific surface area 220 m²/gm and a powder of λ aluminaof specific surface area equal to 320 m²/gm which has been prepared byroasting of bayerite. The proportion of λ alumina is 40% by weight. Thismixture is then formed by extrusion, and then roasted in a current ofdry air at 520° C. for 3 hours

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Lanthanum Deposit

Then the extrusions are put into contact with an aqueous solution oflanthanum nitrate La(No₃)₃, 6H₂O containing 42 gm/l of lanthanum. Thiscontact is carried out at ambient temperature for 2 hours, and then theimpregnated matrix is dried at 120° C. for 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

The platinum and part of the chlorine are then simultaneously depositedon this support through impregnation by a chlorinated aqueous solutioncontaining per liter:

8.20 gm of chlorine in the form of HCl, and

1.00 gm of platinum in the form of H₂PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

e) Deposit of Rhenium and Chlorine

The rhenium and the rest of the chlorine are then simultaneouslydeposited through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a current of dry air.

f) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. To do so, the catalyst is treated at 510° C/ for 2 hoursin a current of air of 2000 dm³/hr for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 11

The same operating mode as for example 10 are followed to prepare acatalyst comprising the same constituents, except that, in stage c), theimpregnation solution contains 21 gm/l of lanthanum, and thehydrothermal treatment of stage f) is not applied.

The specifications of the catalyst obtained are also given in table 6.

EXAMPLE 12

This example illustrates the production of a catalyst comprising amatrix formed of γ alumina, on which silicon, chlorine, lanthanum,rhenium and platinum are deposited.

For this preparation, the same operating mode as for example 10 isfollowed, but stage f) is not carried out. Only γ alumina is- used instage a) and stage b) is carried out in the same conditions as those ofexample 10, except for the concentration in silicon of the solution,which is 3.2 gm/l. Stages c), d) and e), are carried out as in example10.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 13

The same operating mode as for example 12 is followed to prepare acatalyst comprising the same constituents, but a hydrothermal treatmentis also applied in the same conditions as those in example 10 (stage f).

The chlorine content of the catalyst is 1.08% by weight.

COMPARATIVE EXAMPLE 4

In this example, the same operating mode as for example 10 is followed,but only γ alumina is used in stage a) and stages b) and c) fordepositing silicon and lanthanum and stage f) for hydrothermal treatmentare not applied.

The specifications of the catalyst obtained are also given in table 6.

EXAMPLE 14

This example illustrates the production of a catalyst comprising amatrix formed from a mixture of y alumina and λ alumina comprising 12% λalumina, on which silicon, chlorine, lanthanum, tin and platinum aredeposited.

For this preparation, the same operating mode as in example 10 isfollowed, utilizing in stage a) 12% by weight of λ=0 alumina andcarrying out, instead of stages d) and e), a single simultaneous depositstage of platinum, tin and chlorine through impregnation with achlorinated aqueous solution containing per liter:

0.81 gm of platinum in the form H₂PtCl₆, and

0.96 gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C for 3 hours in a current of dry air.

A hydrothermal treatment is then carried out in the presence of waterand chlorine as in stage f) of example 10, but at 500° C. with molarconcentrations in water and chlorine respectively of 1.5% and 0.02%.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 15

The same operating mode as in example 14 is followed to prepare acatalyst comprising the same constituents, apart from the fact, that instage c), the impregnation solution contains 21 gm/l of lanthanum, andthe final hydrothermal treatment of stage f) in the presence of waterand chlorine is not carried out.

The specifications of the catalyst obtained are also given in table 6.

COMPARATIVE EXAMPLE 5

In this example, the same operating mode as in example 14 is followed,but only γ alumina -is used in stage a), and stages b) and c) fordepositing silicon and lanthanum and the last stage f) for hydrothermaltreatment in the presence of water and chlorine of example 14 are notapplied.

The specifications of the catalyst obtained are given in table 6.

TABLE 6 Proportion Specific Platinum Tin Rhenium Chlorine SiliconLanthanum η alumina surface content content content content contentcontent (weight % area (weight (weight (weight (weight (weight (weightCatalyst of matrix) (m²/gm) %) %) %) %) %) %) Example 10 40 0.23 0 0.241.18 0.028 0.47 Example 11 40 0.22 0 0.24 1.09 0.028 0.11 Example 12 00.24 0.23 1.05 0.035 0.43 Compar. 0 0.23 0 0.25 1.12 0 0 Example 4Example 14 Example 14 12 229 0.24 0.16 0 1.13 0.11 1.70 Example 15 12231 0.24 0.16 0 1.08 0.13 0.82 Compar. 0 219 0.25 0.18 0 1.15 0 0Example 5

EXAMPLE 16

In this example, the catalysts of examples 10 and 13 and of thecomparative example 4 are tested for conversion of a load ofhydrocarbons with the following specifications:

volume mass at 20° C. 0.742 kg/dm³ octane number required ˜41 content ofparaffins 52.2% by weight content of naphthenes 32.4% by weight contentof aromatics 15.4% by weight

The following operating conditions are used:

temperature 490° C. total pressure 1.4 Mpa mass flow of load 3.0 kg/kgof catalyst and per hr.

The performances of the catalysts are recorded in table 7 below, and areexpressed in yields by weight and of the octane number required of thereformed product.

TABLE 7 Yield of re- Hydro- formed gen product yield Aromatics C4(weight (weight yield yield C4 Catalyst %) %) (weight %) (weight %)aromatics Example 10 86.0 3.2 58.9 10.8 0.18 Example 11 85.2 3.2 59.211.6 0.20 Example 12 84.8 3.1 58.7 12.1 0.20 Example 13 85.7 3.2 58.811.1 0.19 Comparative 84.4 3.0 58.4 12.6 0.22 example 4

When comparing the performances of the catalysts of example 10 and thecomparative example 4 on the one hand, and those or the catalysts ofexample 11 and of the comparative example 4 on the other, it is notedthat the catalysts of examples 10 and 11 have performances which are a-clear improvement over the catalyst of prior art (comparative example4).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 10 and 11 are very significantlylower than those observed for the catalyst of the comparative example 4.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4-/aromaticsin the table above, is lower for the two catalysts according to theinvention. The selectivity of the catalysts vis-à-vis the aromaticproducts required will become higher as this relation is lowered

The catalysts of examples 10 and 11 containing, in addition compared tothe catalyst of comparative example 4, λ alumina, silicon and lanthanum,present improved specifications relative to the catalyst of comparativeexample 4, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

When comparing the performances of the catalysts of examples 12 and 13,it is noted that the catalyst of example 13 presents improvedperformance compared with the catalyst of example 12.

In fact, the catalyst of example 13 presents a yield in crackingproducts C4- which is clearly lower and a yield in aromatics which isevidently higher. The relation between yields in cracking products C4—and the yields of aromatic compounds, called C4-/aromatics in the tableabove, is lower for the catalyst of example 13. The selectivity of thecatalysts vis-a-vis the aromatic products required will become higher asthis relation is lowered.

The catalysts of examples 12 and 13 contain, among others, silicon andlanthanum. The catalyst of example 13 has, in addition, been submittedto a hydrothermal treatment. It presents improved specificationsrelative to the catalyst of example 12, notably as far as weakerselectivity of- cracking products is concerned, and thus improvedselectivity for aromatic products.

EXAMPLE 17

In this example, the catalysts of examples 14 and 15 and the comparativeexample 5 are tested for conversion of a load of hydrocarbons with thefollowing specifications:

volume mass at 20° C. 0.736 kg/dm³ octane number required ˜38 content ofparaffins 54.8% by weight content of naphthenes 33.1% by weight contentof aromatics 12.1% by weight

The following operating conditions are used:

temperature 500° C. total pressure 0.40 Mpa mass flow of load 2.0 kg/kgof catalyst duration 100 hr.

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performances obtained after 15 hours of functioning for each ofthese two cycles are recorded in table 8 below.

TABLE 8 Aro- Specific Yield of matics C4 surface reformed Octane yieldyield area product number (weight (weight Catalyst cycle (m²/gm) (weight%) required %) %) Example 14 1 229 90.0 101.0 71.7 6.5 5 224 90.8 100.171.1 5.7 Example 15 1 231 89.2 101.4 71.8 7.2 5 222 90.2 100.3 70.8 6.4Comparative 1 219 88.2 100.9 70.S 8.5 Example 5 5 194 89.4 98.6 67.8 7.5

When comparing the performances of the catalysts of examples 14 and is,with those of the prior art catalyst (comparative example 5), it can beseen that the catalysts of examples 14 and 15 show better yields inaromatics and better octane numbers for the reformed product. It canalso be noted that these improvements are achieved without the yields ofreformed product being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 14 and 15 is muchless than that of the prior art catalyst. This smaller fall isaccompanied by better maintenance of yields in aromatics and octanenumbers.

EXAMPLE 18

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and n alumina, on which silicon,chlorine, zirconium, rhenium and platinum are deposited.

a) Formation of the Matrix in Alumina

The alumina matrix is first prepared by mechanical mixing of a powder ofγ alumina of specific surface area 220 m²/gm and a powder or λ aluminaof specific surface area equal to 320 m²/gm which has been prepared byroasting of bayerite. The proportion of λ alumina is 20% by weight. Thismixture is then formed by extrusion, and then roasted in a current ofdry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Zirconium Deposit

Then the extrusions are put into contact with an aqueous solution ofzirconyl chloride ZrOCl₂, 8H₂O containing 26.7 gm/l of zirconium. Thiscontact is carried out at ambient temperature for 2 hours, and then theimpregnated matrix is dried at 120° C. for 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

The platinum and part of the chlorine are then simultaneously depositedon this support through impregnation by a chlorinated aqueous solutioncontaining per liter:

8.20 gm of chlorine in the form of HCl, and

1.00 gm of platinum in the form of H₂PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

e) Deposit of Rhenium and Chlorine

The rhenium and the rest of the chlorine are then simultaneouslydeposited through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a-current of dry air.

f) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. For this, the catalyst is treated at 510° C. for 2 hoursin a current of 2000 dm³/hr of air for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 9.

EXAMPLE 19

The same operating mode as for example 18 is followed to prepare acatalyst comprising the same constituents, except that in stage c), theimpregnation solution contains 13.3 gm/l of zirconium, and thehydrothermal treatment of stage f) is not applied.

The specifications of the catalyst obtained are also given in table 9.

COMPARATIVE EXAMPLE 6

In this example, the same operating mode as in example 18 is followed,but only γ alumina is used in stage a), and stages b) and c) fordepositing silicon and zirconium and stage f) for hydrothermal treatmentare not applied.

The specifications of the catalyst obtained are also given in table 9.

EXAMPLE 20

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and λ alumina, comprising 8% ofλ alumina, on s which silicon, chlorine, zirconium, tin and platinum aredeposited.

For this preparation, the same operating mode as for example 18 isfollowed, using8% by weight of λ alumina in stage a) and carrying out,instead of stages d) and e), a single stage of simultaneous deposit ofplatinum, tin, and chlorine through impregnation with a chlorinatedaqueous solution containing per liter:

0.81 gm of platinum in the form H₂PtCl₆, and

0.96gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupDort is roasted at 530° C. for 3 hours in a current of dry air.

A hydrothermal treatment is then carried out in the presence of waterand chlorine as in stage f) of example 18.

The specifications of the catalyst obtained are given in table 9.

EXAMPLE 21

The same operating mode as for example 20 is followed to prepare acatalyst comprising the same constituents, but in stage c), theimpregnation solution contains 13.3 gm/l of zirconium, and the finalhydrothermal treatment in the presence of water and chlorine is notcarried out.

The-specifications of the catalyst obtained are also given in table 9.

COMPARATIVE EXAMPLE 7

In this example, the same operating mode as for example 20 is followed,but only γ alumina is used in stage a) and stages b) and c) fordepositing silicon and zirconium and the last stage f) for hydrothermaltreatment in the presence of water and chlorine one does not carriedout.

The specifications of the catalyst obtained are also given in table 9.

TABLE 9 Proportion Specific Platinum Tin Rhenium Chlorine SiliconZirconium η alumina surface content content content content contentcontent (weight % area (weight (weight (weight (weight (weight (weightCatalyst of matrix) (m²/gm) %) %) %) %) %) %) Example 18 20 0.24 0 0.261.16 0.032 0.51 Example 19 20 0.23 0 0.23 1.05 0.032 0.15 Compar. 0 0.230 0.25 1.12 0 0 Example 6 Example 20 8 223 0.22 0.17 0 1.12 0.12 1.72Example 21 8 226 0.25 0.15 0 1.05 0.14 0.85 Compar. 0 219 0.24 0.18 01.15 0 0 Example 7

EXAMPLE 22

In this example, the catalysts of examples 18 and 19 and of thecomparative example 6 are tested for conversion of a load ofhydrocarbons with the following specifications:

volume mass at 20° C. 0.742 kg/dm³ octane number required ˜41 content ofparaffins 52.2% by weight content of naphthenes 32.4% by weight contentof aromatics 15.4% by weight

The following operating conditions are used:

temperature 505° C. total pressure 1.3 Mpa mass flow of load 4.0 kg/kgof catalyst and per hr. duration 100 hr.

The performances of the catalysts are recorded in table 10 below, andare expressed in yields by weight and of the octane number required ofthe reformed product.

TABLE 10 Yield of re- Hydro- formed gen product yield Aromatics C4(weight (weight yield yield C4 Catalyst %) %) (weight %) (weight %)aromatics Example 18 86.0 3.2 60.4 10.8 0.18 Example 19 85.2 3.2 61.111.5 0.19 Comparative 84.4 3.0 59.8 12.8 0.21 example 6

When comparing the performances of the catalysts of example 18 and ofthe comparative example 6 on the one hand, and those of the catalysts ofexample 19 and of the comparative example 6 on the other, it is notedthat the catalysts of examples 18 and 19 have performances which are aclear improvement over the catalyst of prior art (comparative example6).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 18 and 19 are very significantlylower than those observed for the catalyst of the comparative example 6.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4/aromatics inthe table above, is lower for the two catalysts of examples 18 and 19.The selectivity of the catalysts vis-à-vis the aromatic productsrequired will become higher as this relation is lowered.

The catalysts of examples 18 and 19 containing, in addition to thecatalyst of comparative example 6, λ alumina, silicon and zirconium,present improved specifications relative to the catalyst of comparativeexample 6, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

EXAMPLE 23

In this example, the catalysts of examples 20 and 21 and of thecomparative example 7 are tested for conversion of a load ofhydrocarbons with the following specifications:

volume mass at 20° C. 0.742 kg/dm³ octane number required ˜41 content ofparaffins 44.2% by weight content of naphthenes 39.4% by weight contentof aromatics 16.4% by weight

The following operating conditions are used:

temperature 505° C. total pressure 0.75 Mpa mass flow of load 2.5 kg/kgof catalyst duration 100 hr.

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then, afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performances obtained after 15 hours of functioning for each ofthese two cycles are recorded in table 11 below.

TABLE 11 Aro- Specific Yield of matics surface reformed Octane yield C4area product number (weight (weight Catalyst cycle (m²/gm) (weight %)required %) %) Example 20 1 223 89.7 102.1 73.3 6.6 5 212 90.7 100.771.9 5.8 Example 21 1 226 90.4 101.9 73.6 5.9 5 209 90.7 100.5 71.6 5.7Comparative 1 219 89.2 102.0 72.8 7.3 Example 7 5 196 90.2 100.2 70.76.4

When comparing the performances of the catalysts of examples 20 and 21,with those of the prior art catalyst (comparative example 7), it can beseen that the catalysts of examples 20 and 21 present better yields inaromatics and better octane numbers for the reformed product. It canalso be noted that these improvements are achieved without the yields ofreformed product being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 20 and 21 is much isless than that of the prior art catalyst. This smaller fall isaccompanied by better maintenance of yields in aromatics and octanenumbers.

The process of the invention thus makes it possible to improvesubstantially the results obtained by the conversion of hydrocarbonsinto aromatic components, in terms of selectivity and stability duringthe reaction cycles.

What is claimed is:
 1. A process for preparing a catalyst, whichcomprises: (a) extruding a matrix of a mixture of λ transition aluminaand γ transition alumina; (b) depositing the following constituents onat least one of the λ and γ transition aluminas, wherein the percentagesby weight are given are based on the total weight of the catalyst; from0.01 to 2% by weight of silicon, from 0.1 to 15% by weight of at leastone halogen selected from the group consisting of fluorine, chlorine,bromine and iodine, from 0.01 to 2% of at least noble metal selectedfrom the platinum group, from 0.005 to 10% by weight of at least onepromoter metal selected from the group consisting of tin, germanium,indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium,molybdenum and tungsten, and optionally, from 0.001 to 10% by weight ofat least one doping metal selected from the group consisting of alkalimetal, alkaline earth metals, lanthanide series metals, titanium,zirconium, hafnium, cobalt, nickel and zinc; and (c) hydrothermallytreating the catalyst obtained after steps (a) and (b) at a temperatureof from 300 to 1000° C. in a gaseous atmosphere containing water vapor,wherein the molar content of water in the gaseous atmosphere is at least0.05%; and wherein step (b) is prior to step (a); and wherein thecatalyst, comprises: a matrix consisting of from about 1 to 99% byweight of λ transition alumina, the complement, up to 100% by weight ofthe matrix, being γ transition alumina; and, based on the total weightof the catalyst: from 0.01 to 2% by weight of silicon, from 0.1 to 15%by weight of at least one halogen selected from the group consisting offluorine, chlorine, bromine and iodine; from 0.01 to 2.00% by weight ofat least one noble metal selected from the platinum group, from 0.005 to10% by weight of at least one promoter metal selected from the groupconsisting of tin, germanium, indium, gallium, thallium, antimony, lead,rhenium, manganese, chromium, molybdenum and tungsten, and optionally,from 0.001 to 10% by weight of at least one doping metal selected fromthe group consisting of alkali metal, alkaline earth metals, lanthanideseries metals, titanium, zirconium, hafnium, cobalt, nickel and zinc,said catalyst having been hydrothermally treated at a temperature of 300to 1000° C. in a gaseous atmosphere containing water vapor, wherein themolar content of water in the gaseous atmosphere is at least 0.05%. 2.The process according to claim 1, wherein the depositing step (b) iscarried out by impregnation using at least one solution containing atleast one precursor compound of a constituent to be deposited, followedby calcination at a temperature of from 300° to 900° C.
 3. The processaccording to claim 1, comprising the following successive stages: (a)extruding the matrix of said mixture of γ alumina and Ti alumina; (b₁)depositing the silicon on the matrix; (b₂) optionally, depositing saidat least one doping metal; (b₃) simultaneous or successive depositingof: at least one promoter metal selected from the group consisting oftin, germanium, indium, gallium, thallium, antimony, lead, rhenium,manganese, chromium, molybdenum and tungsten, at least one elementselected from the group consisting of fluorine, chlorine, bromine andiodine, and at least one noble metal selected from the platinum group;and step (c); and wherein each of steps (b₁), (b₂) or (b₃) is beforestep (a).
 4. The process according to claim 1, wherein the hydrothermaltreatment of step c) is carried out for a period of 1 minute to 30 hoursunder a gaseous atmosphere having a molar water content of 0.05 to 100%.5. The process according to claim 4, wherein the molar content is 1 to50%.
 6. The process according to claim 4, wherein the duration ofhydrothermal treatment is from 1 to 10 hours.
 7. The process accordingto claim 1, wherein the gaseous atmosphere is air, oxygen, argon ornitrogen.
 8. The process according to claim 7, wherein the gaseousatmosphere further comprises at least one halogen.
 9. The processaccording to claim 8, wherein the halogen content of the gaseous mixtureis at most 20 molar %.
 10. The process according to claim 9, wherein thehalogen content of the gaseous mixture is at most 10 molar %.
 11. Theprocess according to claim 10, wherein the halogen content of thegaseous mixture is at most 2 molar %.
 12. A process for preparing acatalyst, which comprises: (a) extruding a matrix of a mixture of λtransition alumina and γ transition alumina; (b) depositing thefollowing constituents on at least one of the λ and γ transitionaluminas, wherein the percentages by weight given are based on the totalweight of the catalyst: from 0.01 to 2% by weight of silicon, from 0.1to 15% by weight of at least one halogen selected from the groupconsisting of fluorine, chlorine, bromine and iodine, from 0.01 to 2% ofat least noble metal selected from the platinum group, from 0.005 to 10%by weight of at least one promoter metal selected from the groupconsisting of tin, germanium, indium, gallium, thallium, antimony, lead,rhenium, manganese, chromium, molybdenum and tungsten, and optionally,from 0.001 to I0% by weight of at least one doping metal selected fromthe group consisting of alkali metal, alkaline earth metals, lanthanideseries metals, titanium, zirconium, hafnium, cobalt, nickel and zinc;and (c) hydrothermally treating the catalyst obtained after steps (a)and (b) at a temperature of from 300 to 1000° C. in a gaseous atmospherecontaining water vapor, wherein the molar content of water in thegaseous atmosphere is at least 0.05%; wherein a portion of theconstituents are deposited prior to step (a) and the remainingconstituents are deposited after step (a); and wherein the catalyst,comprises: a matrix consisting of from about 1 to 99% by weight of λtransition alumina, the complement, up to 100% by weight of the matrix,being γ transition alumina; and, based on the total weight of catalyst:from 0.01 to 2% by weight of silicon, from 0.1 to 15% by weight of atleast one halogen selected from the group consisting of fluorine,chlorine, bromine and iodine, from 0.01 to 2.00% by weight of at leastone noble metal selected from the platinum group, and from 0.005 to 10%by weight of at least one promoter metal selected from the groupconsisting of tin, germanium, indium, gallium, thallium, antimony, lead,rhenium, manganese, chromium, molybdenum and tungsten, and optionally,from 0.001 to 10% by weight of at least are doping metal selected fromthe group consisting of alkali metal, alkaline earth metals, lanthanideseries metals, titanium, zirconium, hafnium, cobalt, nickel and zinc,said catalyst having been hydrothermally treated at a temperature of 300to 1000° C. in a gaseous atmosphere containing water vapor, wherein themolar content of water in the gaseous atmosphere is at least 0.05%. 13.The process according to claim 12, wherein the depositing step b) iscarried out by impregnation using at least one solution containing atleast one precursor compound of a constituent to be deposited, followedby calcination at a temperature of from 300° to 900° C.
 14. The processaccording to claim 12, comprising the following successive stages: (a)extruding the matrix of said mixture of γ alumina and λ alumina; (b₁)depositing the silicon on the matrix; (b₂) optionally, depositing saidat least one doping metal; (b₃) simultaneous or successive depositingof: at least one promoter metal selected from the group consisting oftin, germanium, indium, gallium, thallium, antimony, lead, rhenium,manganese, chromium, molybdenum and tungsten, at least one elementselected from the group consisting of fluorine, chlorine, bromine andiodine, and at least one noble metal selected from the platinum group;and step (c).
 15. The process according to claim 12, wherein thehydrothermal treatment is carried out for a period of 1 minute to 30hours under a gaseous atmosphere having a molar water content of 0.05 to100%.
 16. The process according to claim 15, wherein the molar contentis 1 to 50%.
 17. The process according to claim 15, wherein the durationof hydrothermal treatment is from 1 to 10 hours.
 18. The processaccording to claim 12, wherein the gaseous atmosphere is air, oxygen,argon or nitrogen.
 19. The process according to claim 18, wherein thegaseous atmosphere further comprises at least one halogen.
 20. Theprocess according to claim 19, wherein the halogen content of thegaseous mixture is at most 20 molar %.
 21. The process according toclaim 20, wherein the halogen content of the gaseous mixture is at most10 molar %.
 22. The process according to claim 21, wherein the halogencontent of the gaseous mixture is at most 2 molar %.
 23. A process forpreparing a catalyst, which comprises: (a) extruding a matrix of amixture of λ transition alumina and γ transition alumina; (b) depositingthe following constituents on at least one of the λ and γ transitionaluminas, wherein the percentages by weight given are based on the totalweight of the catalyst: from 0.01 to 2% by weight of silicon, from 0.1to 15% by weight of at least one halogen selected from the groupconsisting of fluorine, chlorine, bromine and iodine, from 0.01 to 2% ofat least noble metal selected from the platinum group, from 0.005 to 10%by weight of at least one promoter metal selected from the groupconsisting of tin, germanium, indium, gallium, thallium, antimony, lead,rhenium, manganese, chromium, molybdenum and tungsten, and optionally,from 0.001 to 10% by weight of at least one doping metal selected fromthe group consisting of alkali metal, alkaline earth metals, lanthanideseries metals, titanium, zirconium, hafnium, cobalt, nickel and zinc;and (c) hydrothermally treating the catalyst obtained after steps (a)and (b) at a temperature of from 300 to 1000° C. in a gaseous atmospherecontaining water vapor, wherein the molar content of water in thegaseous atmosphere is at least 0.05%; wherein the gaseous atmospherefurther comprises at least one halogen; and wherein the catalystcomprises: a matrix consisting of from about I to 99% by weight of λtransition alumina, the complement, up to 100% by weight of the matrix,being γ transition alumina; and, based on the total weight of catalyst:from 0.01 to 2% by weight of silicon, from 0.1 to 15% by weight of atleast one halogen selected from the group consisting of fluorine,chlorine, bromine and iodine, from 0.01 to 2.00% by weight of at leastone noble metal selected from the platinum group, and from 0.005 to 10%by weight of at least one promoter metal selected from the groupconsisting of tin, germanium, indium, gallium, thallium, antimony, lead,rhenium, manganese, chromium, molybdenum and tungsten, said catalysthaving been hydrothermally treated at a temperature of 300 to 1000° C.in a gaseous atmosphere containing water vapor, wherein the molarcontent of water in the gaseous atmosphere is at least 0.05%.
 24. Theprocess according to claim 23, wherein the depositions are carried outby impregnation using at least one solution containing at least oneprecursor compound of a constituent to be deposited, followed bycalcination at a temperature of from 300° to 900° C.
 25. The processaccording to claim 23, comprising the following successive stages: (a)extruding the matrix of said mixture of γ alumina and TI alumina; (b₁)depositing the silicon on the matrix; (b₂) optionally, depositing saidat least one doping metal; (b3) simultaneous or successive depositingof: at least one promoter metal selected from the group consisting oftin, germanium, indium, gallium, thallium, antimony, lead, rhenium,manganese, chromium, molybdenum and tungsten, at least one elementselected from the group consisting of fluorine, chlorine, bromine andiodine, and at least one noble metal selected from the platinum group;and step (c).
 26. The process according to claim 23, wherein thehydrothermal treatment is carried out for a period of 1 minute to 30hours under a gaseous atmosphere having a molar water content of 0.05 to100%.
 27. The process according to claim 26, wherein the molar contentis 1 to 50%.
 28. The process according to claim 26, wherein the durationof hydrothermal treatment is from 1 to 10 hours.
 29. The processaccording to claim 23, wherein the halogen content of the gaseousatmosphere is at most 20 molar %.
 30. The process according to claim 29,wherein the halogen content of the gaseous atmosphere is at most 10molar %.
 31. The process according to claim 30, wherein the halogencontent of the gaseous atmosphere is at most 2 molar %.
 32. The processaccording to claim 23, wherein the catalyst matrix contains from 3.0 to70% by weight of the λ transition alumina.
 33. The process according toclaim 23, wherein the catalyst contains from 0.001 to 8% by weight,based on the total weight of the catalyst, of at least one doping metalselected from the group consisting of alkali metals and alkaline earthmetals.
 34. The process according to claim 33, wherein the doping metalis potassium.
 35. The process according to claim 23, containing from0.01 to 10% by weight based on the total weight of the catalyst, of atleast one doping metal selected from the group consisting of titanium,zirconium, hafnium, cobalt, nickel and zinc.
 36. The process accordingto claim 23, wherein the doping metal is zirconium.
 37. The processaccording to claim 23, further comprising, from 0.001 to 10% by weight,based on the total weight of the catalyst, of at least one doping metalselected from the lanthanide metals.
 38. The process according to claim37, wherein the doping metal is lanthanum.
 39. The process according toclaim 23, wherein the silicon content is from 0.01 to 1% by weight. 40.The process according to claim 23, wherein the halogen content is from0.2 to 10% by weight.
 41. The process according to claim 23, wherein thetotal content of the noble metal is from 0.1 to 0.8% by weight.
 42. Theprocess according to claim 23, wherein the promoter is selected from thegroup consisting of tin, germanium, indium, antimony, lead, thallium,and gallium.
 43. The process according to claim 23, wherein the promotermetal is selected from the group consisting of rhenium, manganese,chromium, molybdenum, tungsten, indium and thallium.
 44. The processaccording to claim 42, wherein the promoter metal is tin.
 45. Theprocess according to claim 23, wherein the halogen is chlorine.
 46. Theprocess according to claim 23, wherein the noble metal is platinum. 47.The process according to claim 23, wherein step (a) is prior to step(b).
 48. The process according to claim 23, wherein step (b) is prior tostep (a).
 49. The process according to claim 23, wherein a portion ofsaid constituents are deposited prior to step (a) and the remainingconstituents are deposited after step (a).
 50. The process according toclaim 23, wherein the depositions are carried out by impregnation usingat least one solution containing at least one precursor compound of aconstituent to be deposited, followed by calcination at a temperature offrom 300° to 900° C.
 51. The process according to claim 23, comprisingthe following successive stages: (a) extruding the matrix of saidmixture of γ alumina and λ alumina; (b₁) depositing the silicon on thematrix; (b₂) optionally, depositing said at least one doping metal; (b3)simultaneous or successive depositing of: at least one promoter metalselected from the group consisting of tin, germanium, indium, gallium,thallium, antimony, lead, rhenium, manganese, chromium, molybdenum andtungsten, at least one selected from the group consisting of fluorine,chlorine, bromine and iodine, and at least one noble metal selected fromthe platinum group; and step (c).
 52. The process according to claim 23,wherein the hydrothermal treatment is carried out for a period of 1minute and 30 hours under a gaseous atmosphere having a molar watercontent of 0.05 to 100%.
 53. The process according to claim 52, whereinthe molar content is I to 50%.
 54. The process according to claim 52,wherein the duration of hydrothermal treatment is from 1 to 10 hours.55. The process according to claim 23, wherein the gaseous atmospherefurther comprises at least one halogen.